Abstract:

Systems and methods for touch screens with integrated transparent
conductive material resistors are provided. Metal traces on the surface
of a touch screen may be subject to radio-frequency interference (RFI)
that can adversely affect the performance of the touch screen.
Transparent conductive material resistors inserted within the metal trace
paths can be used to form low-pass filters which can reduce the affect of
the RFI.

Claims:

1. A touch panel having integrated transparent conductive material
resistors, comprising:a set of transparent conductive material traces on
a first surface of the touch panel;a plurality of metal traces connected
to the set of transparent conductive material traces; anda plurality of
transparent conductive material resistors connected to the metal traces.

2. The touch panel of claim 1, wherein the transparent conductive material
resistors are connected between the metal traces and capacitive sensing
circuitry.

12. A computer system having a touch panel with integrated transparent
conductive material resistors, comprising:a processor configured to
execute instructions and to carry out operations associated with the
computer system;a display device that is operatively coupled to the
processor;a touch panel that is operatively coupled to the processor, the
touch panel being a substantially transparent panel that is positioned in
front of the display, the touch panel comprising:a set of transparent
conductive material traces on a first surface of the touch panel;a
plurality of metal traces connected to the set of transparent conductive
material traces; anda plurality of transparent conductive material
resistors connected to the metal traces.

13. The computer system of claim 12, wherein the transparent conductive
material resistors are connected between the metal traces and capacitive
sensing circuitry.

23. A method for fabricating a touch panel having transparent conductive
material resistors, comprising:forming transparent conductive material
traces on a first surface of the touch panel;forming a plurality of metal
traces connected to the set of transparent conductive material
traces;breaking the metal traces; andforming transparent conductive
material resistors within the breaks of the metal traces.

[0002]There exist many styles of input devices for performing operations
in a computer system. The operations generally correspond to moving a
cursor and/or making selections on a display screen. By way of example,
the input devices may include buttons or keys, mice, trackballs, touch
pads, joy sticks, touch screens and the like. Touch screens, in
particular, are becoming increasingly popular because of their ease and
versatility of operation as well as to their declining price. Touch
screens allow a user to make selections and move a cursor by simply
touching the display screen via a finger or stylus. In general, the touch
screen recognizes the touch and position of the touch on the display
screen and the computer system interprets the touch and thereafter
performs an action based on the touch event.

[0003]Touch screens typically include a touch panel, a controller and a
software driver. The touch panel is a clear panel with a touch sensitive
surface. The touch panel is positioned in front of a display screen so
that the touch sensitive surface covers the viewable area of the display
screen. The touch panel registers touch events (the touching of fingers
or other objects upon a touch sensitive surface) and sends these signals
to the controller. The controller processes these signals and sends the
data to the computer system. The software driver translates the touch
events into computer events.

[0004]Touch panels can include an array of touch sensors capable of
detecting touch events. Some touch panels can detect multiple touches
(the touching of fingers or other objects upon a touch-sensitive surface
at distinct locations at about the same time) and near touches (fingers
or other objects within the near-field detection capabilities of their
touch sensors), and identify and track their locations. Those touch
panels capable of detecting multiple touches may be referred to as
multi-touch panels.

[0005]Mutual capacitive touch panels can be formed from rows and columns
of traces on opposite sides of a dielectric. At the "intersections" of
the traces, where the traces pass above and below each other (but do not
make direct electrical contact with each other), the traces essentially
form two electrodes with a mutual capacitance therebetween. To scan a
sensor panel, a stimulus can be applied to one row with all other rows
held at DC voltage levels. When a row is stimulated, a modulated output
signal can be capacitively coupled onto the columns of the sensor panel.
The columns can be connected to analog channels (also referred to herein
as event detection and demodulation circuits). When the panel is touched
or nearly-touched, a small amount of charge is drawn to the point of
contact. For every row that is stimulated, each analog channel connected
to a column generates an output value representative of an amount of
change in the modulated output signal due to a touch or hover event
occurring at the sensor located at the intersection of the stimulated row
and the connected column. After analog channel output values are obtained
for every column in the sensor panel, a new row is stimulated (with all
other rows once again held at DC voltage levels), and additional analog
channel output values are obtained. When all rows have been stimulated
and analog channel output values have been obtained, the sensor panel is
said to have been "scanned," and a complete "image" of touch or hover can
be obtained over the entire sensor panel. This image of touch or hover
can include an analog channel output value for every pixel (row and
column) in the panel, each output value representative of the amount of
touch or hover that was detected at that particular location.

[0006]Metal traces that are etched into the touch panels can be used to
transmit charges from the panel surface to the event detection and
demodulation circuits connected to the panel. As the size of a touch
screen increases, the length of the metal traces etched into the touch
panel also increases. These longer metal traces can act as antennas and
cause radio-frequency interference (RFI) signals to be brought into the
touch panel circuits and controller. RFI is any undesirable RF signal
that interferes with the integrity of electronics and electrical systems.
These RFI signals may adversely affect the operation of the touch screen.

[0007]Accordingly, what is needed are systems and methods for reducing the
affect of RFI signals in touch screens.

SUMMARY OF THE INVENTION

[0008]Systems and methods for touch screens with transparent conductive
material resistors are provided.

[0009]Transparent conductive material resistors can be inserted into the
metal traces that are etched into the touch panels which are used to
transmit charges from the panel surface to the capacitance detection
circuitry connected to the panel. For example, the metal traces can be
broken and transparent conductive material resistors can be formed inside
these breaks. The resistance of these transparent conductive material
resistors in combination with the inherent capacitance values of the
circuitry and connectors that are connected to the touch panel can form a
low-pass filter that is capable of blocking the RFI signals.

[0010]Inserting the transparent conductive material resistors within the
metal traces in this manner can be accomplished with little or no
incremental cost because the transparent conductive material may already
be patterned on the surface of the touch panel to create the electrode
rows and columns used to form the touch sensors. These electrode rows and
columns are generally formed by depositing a transparent conductive
material layer over the substrate surface, and then by etching away
portions of the transparent conductive material layer in order to form
the traces. Therefore, the transparent conductive material resistors can
be formed as part of the process of creating the transparent conductive
material electrode rows and columns. Instead of etching away all of the
extra portions of the transparent conductive material layer, some of the
transparent conductive material portions may be kept to serve as
transparent conductive material resistors.

BRIEF DESCRIPTION OF THE DRAWINGS

[0011]The above and other features of the present invention, its nature
and various advantages will become more apparent upon consideration of
the following detailed description, taken in conjunction with the
accompanying drawings, in which like reference characters refer to like
parts throughout, and in which:

[0012]FIG. 1 shows an exemplary touch screen computing system operable
with a capacitive touch panel in accordance with an embodiment of the
present invention.

[0013]FIG. 2 shows an exploded perspective view of an illustrative touch
screen computing system in accordance with an embodiment of the present
invention.

[0014]FIG. 3 shows a detailed cross-sectional view of an illustrative
touch screen in accordance with an embodiment of the present invention.

[0015]FIG. 4 shows an illustrative capacitive touch panel with integrated
transparent conductive material resistors in accordance with an
embodiment of the present invention.

[0016]FIG. 5 shows an illustrative touch panel with integrated transparent
conductive material resistors in which the flex circuits are bonded to
the same edge, on directly opposite sides of the panel in accordance with
an embodiment of the present invention.

[0017]FIG. 6 shows an illustrative touch panel with integrated transparent
conductive material resistors in which the flex circuits are bonded to
the same edge, on the same side of the panel in accordance with an
embodiment of the present invention.

[0018]FIG. 7 shows a single illustrative indium tin oxide (ITO) electrode
column that is connected to a capacitive sensing circuit via a metal
trace, an ITO resistor and a flex circuit in accordance with an
embodiment of the present invention.

[0019]FIG. 8 shows a schematic illustration of the elements of FIG. 7 in
accordance with an embodiment of the present invention.

[0020]FIGS. 9 and 10 show two exemplary configurations for connecting a
flex circuits to metal traces having integrated transparent conductive
material resistors in accordance with an embodiment of the present
invention.

[0021]FIG. 1 shows a flowchart of an illustrative process for fabricating
a touch panel with integrated transparent conductive material resistors
in accordance with an embodiment of the present invention.

[0025]FIG. 1 shows an exemplary touch screen computing system 100 operable
with capacitive touch panel 124 according to embodiments of this
invention. Touch panel 124 can be connected to other components in
computing system 100 through connectors integrally formed on the sensor
panel, or using flex circuits. Computing system 100 can include one or
more panel processors 102 and peripherals 104, and panel subsystem 106.
The one or more processors 102 can include, for example, ARM968
processors or other processors with similar functionality and
capabilities. However, in other embodiments, the panel processor
functionality can be implemented instead by dedicated logic such as a
state machine. Peripherals 104 can include, but are not limited to,
random access memory (RAM) or other types of memory or storage, watchdog
timers and the like.

[0026]Panel subsystem 106 can include, but is not limited to, one or more
analog channels 108, channel scan logic 110 and driver logic 114. Channel
scan logic 110 can access RAM 112, autonomously read data from the analog
channels and provide control for the analog channels. This control can
include multiplexing columns of multi-touch panel 124 to analog channels
108. In addition, channel scan logic 110 can control the driver logic and
stimulation signals being selectively applied to rows of multi-touch
panel 124. In some embodiments, panel subsystem 106, panel processor 102
and peripherals 104 can be integrated into a single application specific
integrated circuit (ASIC).

[0027]Driver logic 114 can provide multiple panel subsystem outputs 116
and can present a proprietary interface that drives high voltage driver
118. High voltage driver 118 can provide level shifting from a low
voltage level (e.g. complementary metal oxide semiconductor (CMOS)
levels) to a higher voltage level, providing a better signal-to-noise
(S/N) ratio for noise reduction purposes. The high voltage driver outputs
can be sent to decoder 120, which can selectively connect one or more
high voltage driver outputs to one or more panel row inputs 122 through a
proprietary interface and enable the use of fewer high voltage driver
circuits in the high voltage driver 118. Each panel row input 122 can
drive one or more rows in a multi-touch panel 124. In some embodiments,
high voltage driver 118 and decoder 120 can be integrated into a single
ASIC®. However, in other embodiments high voltage driver 118 and
decoder 120 can be integrated into driver logic 114, and in still other
embodiments high voltage driver 118 and decoder 120 can be eliminated
entirely.

[0028]Computing system 100 can also include host processor 128 for
receiving outputs from panel processor 102 and performing actions based
on the outputs that can include, but are not limited to, moving an object
such as a cursor or pointer, scrolling or panning, adjusting control
settings, opening a file or document, viewing a menu, making a selection,
executing instructions, operating a peripheral device connected to the
host device, answering a telephone call, placing a telephone call,
terminating a telephone call, changing the volume or audio settings,
storing information related to telephone communications such as
addresses, frequently dialed numbers, received calls, missed calls,
logging onto a computer or a computer network, permitting authorized
individuals access to restricted areas of the computer or computer
network, loading a user profile associated with a user's preferred
arrangement of the computer desktop, permitting access to web content,
launching a particular program, encrypting or decoding a message, and/or
the like. Host processor 128 can also perform additional functions that
may not be related to panel processing, and can be coupled to program
storage 132 and display device 130 such as a liquid crystal display (LCD)
for providing a UI to a user of the device.

[0029]As mentioned above, multi-touch panel 124 can in some embodiments
include a capacitive sensing medium having a plurality of row traces or
driving lines and a plurality of column traces or sensing lines separated
by a dielectric. In some embodiments, the dielectric material can be
transparent, such as polyethylene terephthalate (PET), glass, or another
material such as Mylar. The row and column traces can be formed from a
transparent conductive material such as indium tin oxide (ITO),
conductive clear polymer, or antimony tin oxide (ATO), although other
non-transparent materials such as copper can also be used. In some
embodiments, the row and column traces can be perpendicular to each
other, although in other embodiments other non-orthogonal orientations
are possible. For example, in a polar coordinate system, the sensing
lines can be concentric circles and the driving lines can be radially
extending lines (or vice versa). It should be understood, therefore, that
the terms "row" and "column," "first dimension" and "second dimension,"
or "first axis" and "second axis" as may be used herein are intended to
encompass not only orthogonal grids, but the intersecting traces of other
geometric configurations having first and second dimensions (e.g. the
concentric and radial lines of a polar-coordinate arrangement).

[0030]At the "intersections" of the traces, where the traces pass above
and below each other (but do not make direct electrical contact with each
other), the traces essentially form two electrodes (although more than
two traces can intersect as well). Each intersection of row and column
traces can represent a capacitive sensing node and can be viewed as
picture element (pixel) 126, which can be particularly useful when
multi-touch panel 124 is viewed as capturing an "image" of touch. (In
other words, after panel subsystem 106 has determined whether a touch
event has been detected at each touch sensor in multi-touch panel 124,
the pattern of touch sensors in the multi-touch panel at which a touch
event occurred can be viewed as an "image" of touch (e.g. a pattern of
fingers touching the panel).) When the two electrodes are at different
potentials, each pixel can have an inherent self or mutual capacitance
formed between the row and column electrodes of the pixel. If an AC
signal is applied to one of the electrodes, such as by exciting the row
electrode with an AC voltage at a particular frequency, an electric field
and an AC or signal capacitance can be formed between the electrodes,
referred to as Csig. The presence of a finger or other object near or on
multi-touch panel 124 can be detected by measuring changes to Csig. The
columns of multi-touch panel 124 can drive one or more analog channels
108 in panel subsystem 106. In some embodiments, each column is coupled
to one dedicated analog channel 108. However, in other embodiments, the
columns can be couplable via an analog switch to a fewer number of analog
channels 108.

[0031]FIG. 2 shows an exploded perspective view of an illustrative touch
screen computing system 200. Touch screen system 200 includes liquid
crystal display (LCD) 230 and transparent touch screen 220 positioned in
front of LCD 230. LCD 230 can be configured to display a graphical user
interface (GUI) including perhaps a pointer or cursor as well as other
information to a user. Touch screen 220, on the other hand, is an input
device that is sensitive to a user's touch, allowing a user to interact
with the graphical user interface on LCD 230. By way of example, touch
screen 220 may allow a user to move an input pointer or make selections
on the graphical user interface by simply pointing at the GUI on LCD 230.

[0032]Housing 210 encloses and protects touch screen 220, LCD 230, as well
as circuitry 240. Circuitry 240 can include controller circuitry for
touch screen 220, and LCD 230 as well as additional circuitry including
processor circuitry, memory circuitry, and power circuitry. Touch screen
system 200 may be a stand alone unit or it may integrated with other
devices. When stand alone, touch screen system 200 (or each of its
components) can act like a peripheral device that includes its own
housing and that can be coupled to a host device through wired or
wireless connections. When integrated, touch screen system 200 shares
housing 210 and is hard wired into the host device thereby forming a
single unit. By way of example, touch screen system 200 may be disposed
inside a variety of host devices including but not limited to general
purpose computers such as a desktop, laptop or tablet computers,
handhelds such as PDAs and media players such as music players,
peripheral devices such as cameras, printers and/or the like, or hybrid
computer/phone devices.

[0033]FIG. 3 shows a detailed cross-sectional view of illustrative touch
screen 300. Touch screen 300 includes capacitive touch panel 330 which is
sandwiched between protective cover 310 and LCD 340. LCD 340 can
correspond to any conventional LCD display known in the art. Although not
shown, the LCD 340 typically includes various layers including a
fluorescent panel, polarizing filters, a layer of liquid crystal cells, a
color filter and the like.

[0034]Protective cover 310 serves to protect the under layers and provide
a surface for allowing an object to slide thereon. Cover 310 can be
suitably thin to allow for sufficient coupling to capacitive touch panel
330. Cover 310 can be formed from any suitable clear material such as
glass and plastic. In addition, cover 310 can be treated with coatings to
reduce sticktion when touching and reduce glare when viewing the
underlying LCD 310. By way of example, a low sticktion/anti reflective
coating can be applied over the cover sheet 310.

[0035]Touch screen 300 also includes various bonding layers 320. Bonding
layers 320 bond capacitive touch panel to LCD 340 and cover 310 together
to form the laminated structure and to provide rigidity and stiffness to
the laminated structure. In essence, bonding layers 320 help to produce a
monolithic sheet that is stronger than each of the individual layers
taken alone. In some cases, the bonding agent includes an index matching
material to improve the visual appearance of the touch screen 300. In
some embodiments, one or both bonding layers 320 can be eliminated
without affecting the performance of the touch screen.

[0036]FIG. 4 shows an illustrative capacitive touch panel 400 with
integrated transparent conductive material resistors. Touch panel 400
includes a plurality of capacitance sensing nodes 440. The capacitive
sensing nodes may be widely varied. For example, the capacitive sensing
nodes may be based on self capacitance or mutual capacitance. In self
capacitance, the "self" capacitance of a single electrode is measured as
for example relative to ground. In mutual capacitance, the mutual
capacitance between at least first and second electrodes is measured. In
either case, each node 440 can work independent of the other nodes 440 so
as to produce simultaneously occurring signals representative of
different points on the touch panel 400.

[0037]As shown, the touch panel 400 includes a two layer grid of spatially
separated non-overlapping lines. In the illustrated embodiment touch
panel 400 includes transparent conductive material column traces 410 on
the top surface and transparent conductive material row traces 420 on the
bottom surface. In most cases, the lines on each surface are parallel one
another. Furthermore, although in different planes, the lines on the
different surfaces are configured to intersect or cross in order to
produce capacitive sensing nodes 440, which each represent different
coordinates in the plane of the touch panel 400. The nodes 440 are
configured to receive capacitive input from an object touching the touch
panel 400 in the vicinity of the node 440. When an object is proximate to
a node 440, the object steals charge thereby affecting the capacitance at
the node 440.

[0038]As previously described, row traces 420 are individually stimulated
with an AC signal while column traces 410 are connected to capacitive
sensing circuitry (not shown) that may continuously sense all of column
traces 410. The capacitive sensing circuitry typically includes one or
more sensor ICs that measure the capacitance in each of column traces 410
and reports its findings to a host controller. The sensor ICs may, for
example, convert the analog capacitive signals to digital data and
thereafter transmit the digital data over a serial bus to a host
controller. Any number of sensor ICs may be used. For example, a sensor
IC may be used for all column traces 410, or multiple sensor ICs may be
used for a single or group of column traces 410. In most cases, the
sensor ICs report tracking signals, which are a function of both the
position of the node 440 and the intensity of the capacitance at the node
440.

[0039]Column traces 410 and row traces 420 can be placed on the surfaces
of dielectric member 401 using any suitable patterning technique
including for example, deposition, etching, printing and the like.
Because row traces 420 may be either stimulated with an AC signal or held
at a DC voltage level, and because column traces 410 need to be connected
to analog channels so that modulated output signals can be detected,
demodulated and converted to output values, electrical connections must
be formed with row traces 420 and column traces 410.

[0040]Flex circuits can be electrically connected directly to row traces
420 and column traces 410. However, as the size of touch panel 400
increases, the size of the flex circuits required to couple directly to
row traces 420 and column traces 410 also increases. In order to reduce
the size of the flex circuits and to allow for greater variation in the
placement of flex circuits, metal traces 415 and 425 can be used to
connect row traces 420 and column traces 410 to the flex circuits.

[0041]Metal traces 415 and 425 can be beneficial for this arrangement
because they allow the use of compact flex circuits 430 and 460. Flex
circuits 430 and 460 only occupy a small portion of the edges of touch
panel. These flex circuits can be significantly smaller than the size of
flex circuits that would be required to directly couple to row traces 420
and column traces 410. For example, coupling flex circuitry directly to
the row and column traces may require the flex circuits to span nearly
the entire edge of the touch panel. FIGS. 5 and 6 show two other
exemplary arrangements that can be made by using metal traces to couple
electrode rows and electrode columns to their respective flex circuits.

[0042]FIG. 5 shows an illustrative touch panel 500 in which the flex
circuits are bonded to the same edge, on directly opposite sides of
dielectric 501. This arrangement can be made by running metal traces 525
along the edge of dielectric 501. Connecting the flex circuits in this
arrangement can minimize the area of touch panel 500 needed for
connectivity and can reduce the overall size of touch panel 500. Further,
a single flex circuit can be fabricated to connect to rows 520 and
columns 510 on directly opposing sides of the same edge of the substrate.
Connecting the flex circuits in this arrangement can minimize the area of
touch panel 500 needed for connectivity and can reduce the overall size
of touch panel 500.

[0043]FIG. 6 shows an illustrative touch panel 600 in which the flex
circuits are bonded to the same edge, on the same side of dielectric 601.
This arrangement can be made by running metal traces through dielectric
601 in order to connect rows 620 to the top surface of dielectric 601 and
then running metal traces 625 along the edge of the top surface of
dielectric 601. Connecting the flex circuits in this arrangement can
minimize the area of touch panel 600 needed for connectivity and can
reduce the overall size of touch panel 600. Further, a single flex
circuit can be fabricated to connect to rows 620 and columns 610.

[0044]Many other arrangements of flex circuits on the touch panels are
possible through the use of metal traces in this manner. In some
embodiments, both electrode rows and electrode columns can be coupled to
their respective flex circuits using metal traces. In some other
embodiments, only one set of electrodes are couples to their flex circuit
using metal traces. For example, in the embodiment of FIG. 5 rows 520 can
be coupled to a flex circuit using metal traces, while columns 510 can be
coupled directly to their flex circuit.

[0045]While the use of metal traces has many advantages, routing signals
along metal traces 415 and 425 has one drawback. Metal traces 415 and 425
can act like antennas and may cause radio-frequency interference (RFI)
signals to be coupled to the sensing circuits. These RFI signals may
adversely affect the operation of the touch screen and the accuracy at
which touch screen 400 is able to detect user input. As the size of touch
screen 400 increases, the lengths of metal traces 415 and 425 also
increase, thereby increasing the affect of the RFI signals.

[0046]In accordance with this invention, the metal traces can be broken
and resistors 416 and 426 can be inserted into the signal paths in order
to reduce the affect of the RFI signals. Resistors 416 and 426 can
preferably be fabricated using the same transparent conductive material
used to form traces 410 and 420. For example, resistors 416 and 426 may
be formed from ITO.

[0047]FIG. 7 shows a single illustrative ITO column trace 710 that is
connected to a capacitive sensing circuit 750 via a metal trace 726, an
ITO resistor 726 and a flex circuit 730. The ITO may have a sheet
resistivity of approximately 200 Ohms per square unit, making the
resistance of resistor 746 approximately equal to 400 Ohms. It should be
understood that any other suitable transparent conductive material may be
used to form column trace 710 and resistor 726.

[0048]FIG. 8 shows a schematic illustration of the elements of FIG. 7.
Sensing line 820 can be modeled as a continuously distributed
capacitance. The resistivity of metal trace 825 and flex circuit 830 can
be ignored as being negligible. Finally, ITO resistor 826 in conjunction
with capacitor 840 forms a low-pass filter. Capacitor 840 represents the
input capacitance of capacitive sensing circuit 850 as well as the
capacitance of the flex circuitry that is used to couple metal trace 825
to capacitive sensing circuit 850. In this embodiment the capacitance of
capacitor 840 can be approximated as 40 pf. With the proper resistance
values, this low-pass filter can preferably block or at least
significantly attenuate the RFI signals picked up by the metal traces
before they are detected at the capacitive sensing circuit. For example,
a low-pass filter with a capacitance value of 40 pf and a resistance
value of 400 Ohms has a calculated cut-off frequency of 10 MHz. In other
words, the resistance and capacitance combination formed by inserting ITO
resistors into the metal traces of a touch panel can block most signals
with a frequency higher than 1 GHz. This cut-off frequency is suitable to
block most of the RFI from entering the capacitive sensing circuitry. The
size of ITO resistor 826 can be adjusted to obtain an appropriate
resistance value in order to ensure an appropriate cut-off frequency
value.

[0049]Inserting the transparent conductive material resistors within the
metal traces in this manner can be accomplished with little or no
incremental cost because the transparent conductive material may already
be patterned on the surface of the touch panel to create the transparent
conductive material electrode rows and columns. These electrode rows and
columns are generally formed by depositing an transparent conductive
material layer over the substrate surface, and then by etching away
portions of the transparent conductive material layer in order to form
the lines. Therefore the transparent conductive material resistors, in
accordance with the invention, may be formed as part of the process of
creating the electrode rows and columns. Then, instead of etching away
all of the extra portions of the transparent conductive material layer,
some of the portions transparent conductive material may be kept to serve
as transparent conductive material resistors. In some other embodiments,
multiple layers of transparent conductive material may be deposited over
the substrate surface thereby allowing the transparent conductive
material resistors to be formed separately from the electrode rows and
columns. In some embodiments, the transparent conductive material used to
form the resistors can be different than the transparent conductive
material resistors used to form the electrode rows and columns.

[0050]Furthermore, there is an additional benefit to leaving additional
transparent conductive material on the surface of a touch panel. As
should be appreciated, the areas with transparent conductive material
tend to have lower transparency than the areas without transparent
conductive material. This is generally less desirable for the user as the
user can distinguish the lines from the spaces therebetween, i.e., the
patterned transparent conductive material can become quite visible
thereby producing a touch screen with undesirable optical properties. In
order to prevent the aforementioned problem, rather than simply etching
away all of the transparent conductive material, the dead areas (the
uncovered spaces) may be subdivided into unconnected electrically
floating transparent conductive material pads, i.e., the dead areas may
be patterned with spatially separated pads. The pads are typically
separated with a minimum trace width. Furthermore, the pads are typically
made small to reduce their impact on the capacitive measurements. This
technique attempts to minimize the appearance of the transparent
conductive material by creating a uniform optical retarder. That is, by
seeking to create a uniform sheet of transparent conductive material, it
is believed that the panel will function closer to a uniform optical
retarder and therefore non-uniformities in the visual appearance will be
minimized. Thus, in some embodiments, in addition to floating transparent
conductive material pads, transparent conductive material resistor blocks
can be patterned on the surface of the touch panel to provide RFI
blocking as well as increasing the uniformity of the visual appearance of
the touch panel.

[0051]FIGS. 9 and 10 show two exemplary configurations for connecting a
flex circuits to metal traces having integrated transparent conductive
material resistors. In FIG. 9, metal traces 910 are etched into the top
surface of touch panel 900. Near the edge of touch panel 900, metal
traces 910 are broken and transparent conductive material resistors 920
are inserted. After transparent conductive material resistors 920 metal
traces portions 910a continue and are connected to the copper traces of
flex circuit 930. While metal trace portions 910a do not benefit from the
RFI blocking of transparent conductive material resistors 920, these
portions can be made sufficiently short to minimize the affect of the
RFI.

[0052]FIG. 10 shows another configuration for connecting flex circuits to
metal traces having integrated transparent conductive material resistors.
Metal traces 1010 are etched into the top surface of touch panel 1000 and
near the edge of touch panel 1000, metal traces 1010 are broken and
transparent conductive material resistors 1020 are inserted. Transparent
conductive material resistors 1020 are formed sufficiently close to the
edge of touch panel 1000 so that flex circuit 1030 can be bonded directly
to transparent conductive material resistors 1020. Thus, in this
configuration, transparent conductive material resistors 1020 are able to
block the RFI for the entirety of metal traces 1010.

[0053]FIG. 11 shows a flowchart of process 1100 for fabricating a touch
panel with integrated transparent conductive material resistors in
accordance with the present invention. At step 1110 transparent
conductive material traces are formed on a surface of a touch panel. At
step 1120 metal traces are formed to connect the transparent conductive
material traces to a flex circuit connector. At step 1130 the metal
traces are broken and at step 1140 transparent conductive material
resistors are formed within the breaks of the metal traces. While this
invention has been primarily described with reference to breaking metal
traces to form the transparent conductive material resistors, it should
be understood these steps may also be accomplished using any number of
suitable techniques. For example, rather than breaking a metal trace, a
metal trace may be formed having a gap that is sized to accommodate an
transparent conductive material resistor. Furthermore, in some
embodiments, the transparent conductive material layer may be fabricated
before the metal trace layer. In these embodiments, the metal trace
portions may actually be formed around the transparent conductive
material resistors.

[0054]Thus it is seen that the systems and method for fabricating touch
panels with integrated transparent conductive material resistors in
accordance with the present invention are provided. Those skilled in the
art will appreciate that the invention can be practiced by other than the
described embodiments, which are presented for purposes of illustration
rather than of limitation, and the invention is limited only by the
claims which follow.